Fused fibers of monoolefin polymers and method of manufacture



llited States Patent 3,436,298 FUSED FIBERS 0F MONOOLEFIN POLYMERS AND METHOD OF MANUFACTURE George C. Oppenlander, Embreeville, Pa., and Walter W.

Thomas, West Park, Del., assignors to Hercules Incorporated, a corporation of Delaware No Drawing. Filed Dec. 28, 1965, Ser. No. 517,107 Int. Cl. B32b 27/02, 5/22; D04h 1/04 US. Cl. 161150 9 Claims This invention relates to novel structures which are bonded assemblages of polyolefin fibers and to a process for producing the same.

Assemblages of polyolefin fibers have found many uses such as in nonwoven and woven fabrics, backing materials for pile fabrics, filter cloths, tobacco smoke filters, ropes, yarn tapes, clothing insulation, blankets, surgical dressings, inner soles for shoes, gasket material, and the like. For many of these uses it is important that the fibers in the assemblage be interlocked or bonded to other fibers of the structure. This bonding or interlocking of the fibers gives a cohesion to the structure as well as additional strength.

Various methods have been proposed for effecting the bonding or interlocking of the fibers to each other. In one of such methods it has been proposed to heat-seal the fibers to each other. This method, however, has not proved practical for many applications. The use of temperatures high enough to soften fiber surfaces and to form the interfiber bonds needed to develop good strength causes serious damage to fibers, which are dependent on molecular orientation effects for optimum physical properties. In addition, when nonwoven webs of polyolefin fibers are thermally bonded, the heat normally required to soften the surface causes series shrinkage unless costly provisions are used to restrain the web and to prevent shrinkage not only while the web is heated but also subsequently while it is cooled. Even with provision for reducing web shrinkage, as, for example, by bonding in a press and maintaining the pres sure while the web is cooled, undesirable properties are obtained. Depending on the amount of heating used, the bonded webs are either soft and weak, or comparatively strong but harsh and plastic-like. Webs bonded adequately to give acceptable strength fail to have the flexibility and soft, fabric-like properties required for many applications.

In another method it has been proposed to bond the fibers in assemblages by aid of chemical bonding agents or adhesives. The selection of bonding agents for polyolefin fibers, however, has been a difficult problem because the polyolefins are so inert to chemical attack that the adhesives do not provide a quick, strong, and nontacky bond. Furthermore, the use of a bonding agent involves several time-consuming and troublesome handling operations. For example, if the bonding agent is applied as a solution or emulsion, not only is it necessary to spray or dip the individual fibers or the complete assemblage to contact it with the binder, but the liquid phase of the solution or emulsion must be removed. It is usually then necessary to heat or otherwise activate the bonding agent to cure it and adhere it to the fibers.

It has now been found that bonded assemblages of polyolefin fibers can be prepared by a process which avoids all of the above difiiculties. This process comprises forming an assemblage of fibers comprising fibers of a polymer of an zx-monoolefin containing from about 0.2% to about 10% by weight of the polymer of a carboxylic acid salt of a metal selected from the group consisting of calcium, barium, iron, nickel, and cobalt, said salt having a melting temperature below the temperature at which the fiber is 3,436,298 Patented Apr. 1, 1969 spun, heating the assemblage at an elevated temperature which is below the crystalline melting temperature of the polymer but is sufficiently elevated to render the surfaces of said fibers tacky and heat-softened without substantially affecting the fibrous structure and the strength properties of said fibers, and then cooling the assemblage whereby said heat-softened fibers are heat-bonded to other fibers in the assemblage at points of contact therewith. The assemblage can comprise exclusively these so-called metal salt-modified fibers, i.e., fibers of a polymer of an a-monoolefin containing the metal salt of a carboxylic acid, or it can comprise a blend of these metal salt-modified fibers with other fibers, either synthetic or natural, such as, for example, fibers or unmodified polypropylene, polyester, polyamide, acrylic polyers, poly(vinyl chloride), poly(vinylene chloride), viscose or acetate rayon, cotton, glass, and the like, provided, of course, sufiicient of the metal salt-modified fibers are present to accomplish bonding in accordance with the present invention.

The fibers employed in the process of the invention are, as stated above, of polymers of an ot-monoolefin containing from about 0.2% to about 10%, based on the Weight of the polymer, of the metal salt of a carboxylic acid. Particularly useful for these fibers are the homopolyrners, copolymers, and terpolymers of ethylene and a-monoolefins having from 3 to 6 carbon atoms, including, for instance, polyethylene, polypropylene, poly(butene-l), poly(pentene-l), poly(3-methylbutene-l), and poly (4- methylpentene-l), copolymers of ethylene and propylene, terpolymers of ethylene, propylene and diene such as dicyclopentadiene, and the like.

The metal salts of the present invention are calcium, barium, iron, nickel, or cobalt salts of carboxylic acids and have melting temperatures below the temperature at which the fiber is spun. The carboxylic acid component of such salts are organic acids containing one or more carboxyl groups and can be either saturated or unsaturated. Particularly preferred are the aliphatic acids, i.e., acyclic or alicyclic acids containing from 4 to 20 carbon atoms, and most preferably fatty acids containing 8 to 18 carbon atoms. Such salts are known to the art and include, by way of example, salts of isobutyric, isovaleric, caproic, 2- ethylbutyric, Z-methylpentanoic, n-octanoic, 2-ethylhexanoic, 2,2,4,4-tetramethylpentanoic, 2,4,6-trimethylheptanoic, 5,7-dimethyloctanoic, pelargonic, lauric, tridecanoic, myristic, palmitic, stearic, naphtenic, 3-methylcyclohexane carboxylic, 4-isopropylcyclohexane carboxylic, cyclohex ane acetic, bicyclo(2,2,1) heptane carboxylic, octly succinic, Z-decylglutaric, 2,5-dibutyl adipic, sebacic, oleic, linoleic, a-phenyl propionic acid, and the like. The metal salts of mixtures of acids, such as, for example, coconut fatty acids, are also suitable. The salts can be employed as such or can be used as mixtures thereof with other of the metal salts or with the free acid. The use of a 2:1 to 5:1 mixture of the metal salt and a carboxylic acid having 4 to 18 carbon atoms is particularly preferred.

The metal salts can 'be admixed with the polyolefin by any of the usual procedures for incorporating an additive in a solid material. A simple method is to dissolve the metal salt in a low boiling solvent such as benzene. or acetone and, after thoroughly mixing the solution with the polyolefin in flake or other such form, evaporating the solvent; or it can be incorporated by various means of mechanical mixing, as by grinding, milling, or the like.

The amount of the metal salt incorporated in the polyolefin can vary from about 0.2% up to about 10% by weight of the polyolefin, or higher. Normally, a maximum amount of about 4% will be sufiicient to accomplish the objects of the present invention. The optimum amount Will usually be between about 0.4 and about 2%, depending primarily upon the particular metal salt employed and the degree of bonding desired.

The polyolefin can also contain small amounts of stabilizers, such as heat and light stabilizers, ultraviolet light absorbers, antacids such as calcium soaps, antioxidants, and the like, as well as other materials such as pigments, dyes, fillers, and the like, provided they do not interfere with the process of the invention.

The fibers employed in the assemblages of this invention can be monofilaments or multifilaments and are prepared by the well-known procedures normally used for the preparation of synthetic fibers. Briefly, this comprises extruding or spinning the molten polyolefin containing the metal salt through an orifice containing a single hole or a plurality of very fine holes, and then drawing the polymer away from the orifice, preferably at a greater rate than the rate of extrusion to effect a substantial drawdown of the filament in the molten state prior to solidification thereof. The conditions and particularly the temperature for melt-spinning polyolefins into fibers are well known to the art and can vary over a relatively wide range depending upon the physical and chemical properties of the polyolefin and can even vary for identical compositions according to the preference of skilled operators. In general, temperatures within the range of about 200 to about 325 C., and preferably from about 250 to about 300 C., will normally produce a melt of sufficient fluidity to fiow evenly from the orifice. The solidified filaments can then be combined into a multifilament yarn and subjected to a cold draw at a temperature below the melting point whereby a desired amount of molecular orientation is imparted to the fiber. If desired, these molecularly oriented filaments can then be crimped, usually by mechanical means such as a stufling box crimper and/ or chopped into relatively short staple fibers, usually on the order of one to several inches in length.

While the fibers used in the invention can advantageously be prepared by the procedure described above, it must be understood that the process is not so limited. For example, if desired, the molecular orientation step can be omitted if the greater dimensional stability of the unoriented fiber under the influence of heat is desired. Likewise, the crimping step can be omitted if uncrimped fiber is desired, or the chopping step can be omitted if continuous filament is desired.

The invention can be practiced with assemblages of fibers prepared by any method known to the art. Thus, it is applicable to bundles of continuous filament, crimped or otherwise, or of short fibers or staple yarns, nonwoven webs of randomly deposited fibers, nonwoven webs having individual fibers oriented or aligned along a particular axis, woven fabrics of the fibers, knit fabrics of the fiber, groupings of continuous filament laid up parallel to each other, and the like. The invention is especially valuable for nonwoven webs wherein the fibers are randomly deposited since in these webs the entanglement of the fibers yields a greater number of potential bOnding sites, and to needle-punched nonwoven webs wherein the degree of fiber entanglement is even further increased. The fused assemblages of the invention, such as, for example, fused tapes or yarns, can also be used as such or can be knitted or woven, with or without other fibrous materials, into fabrics for such uses as carpet backings and the like.

The type of bond which is produced in the practice of the present invention is unlike the prior art bonds in that it is a unique surface adhesion of fiber to fiber at points of contact between them and is the result of a heatsoftening or tackifying of the surface of the fiber at a temperature below the crystalline melting point of the polymer followed by a cooling, whereby the softened surfaces of the fiber solidify and become bonded to other fibers at points of contact therewith. Just what surface phenomena take place when the assemblage of fibers is heated in accordance with the invention is not thoroughly understood. It is postulated that the presence of the metal salt in the polyolefin fiber may create at the surface of the fiber during heating uniquely reactive or heat-sensitive sites either by exudation or chemical reaction or otherwise, whereby the surface of the fiber becomes selectively tackier and more adherent. No matter what the explanation of the phenomena may be, it is certain that with the metal salt-modified fibers it is possible by the present invention to create well-bonded fibrous structures without adversely affecting the elevated temperature shrinkage and strength properties of the polyolefin fibers.

The heating of the assemblage can be carried out in any desired manner using methods well known to the art, as, for example, using a heated press, hot calender rolls or drum dryers and the like or by heating with hot air, infrared radiation, or high frequency means, i.e., dielectric heating or the like. The temperature at which the assemblage is heated, as stated above, is below the crystalline melting temperature of the polymer but is sufliciently high to heat-soften the surface of the fiber to make it tacky or sticky without at the same time substantially affecting the fibrous structure or strength properties of the fiber. The maximum temperature at which such assemblages can be heated will vary, of course, with the particular polymer employed. Preferably, the maximum temperature will range from about 10 to 15 C. below the crystalline melting point of the polymer since at or below such maximum temperature, optimum structural and strength properties are obtained.

The following examples illustrate the process of the invention and demonstrate the desirable properties of the novel structures produced thereby. The term RSV as used herein denotes reduced specific viscosity, which is the specific viscosity divided by concentration of a 0.1% weight/volume solution of polymer in decahydronaphthalene at 135 C. All parts and percentages are by weight unless otherwise stated, and the percentage of additives is based on the weight of the polymer unless otherwise specified.

EXAMPLE 1 Stereoregular polypropylene having a birefringent melting point of about 172 C. and an RSV of 3.2 and containing 0.15% of the reaction product of 2 moles of nonylphenol and 1 mole of acetone (the reaction product comprising a mixture of isopropylidene-bis(nonylphenol) and 2(2'-hydroxyphenyl) 2,4,4 trimethyl-5,6-dinonyl chroman) as antioxidant, was thoroughly blended with 0.92% of a commercial nickel octate consisting of a 3:1 mixture of nickel-Z-ethylhexanoate and 2-ethylhexanoic acid (total nickel content, 13%). The blend was melt spun into continuous filament yarns (820 denier/35 filament) at 550 F. The fusion temperature of the yarn was determined by plying 4 filaments and then drawing the plied yarn from 220 F. feed rolls at 450 ft./min. onto a pair of 6" diameter heated draw rolls using 13 wraps of the yarn, the draw roll temperature being increased in 10 F. increments until the filaments fused into a ribbon in which the filaments could be stripped apart. The plied yarn, produced as above described, fused at 290 P. whereas a control yarn prepared in the same manner, except that the polypropylene did not contain the nickel salt mixture, fused at 345 F. Increasing the amount of nickel salt mixture in the polymer to 4% did not alter the fusion temperature from 290 F. whereas decreasing the amount to 0.46% gave a fusion temperature 310 F. A carpet backing fabric woven from the fused ribbon (2 mils thick and mils wide) of this example had a good appearance and feel and gave excellent tufting performance.

EXAMPLES 2 to 8 The procedure of Example 1 was repeated except that various amounts of other nickel salts were substituted for the nickel octate mixture of Example 1. The compositions of these examples and the fusion temperatures of the ribbons therefrom are tabulated below.

6 TABLE I What we claim and desire to protect by Letters Patent is: Nickels, additive ,Zgjffi, 1. As an article of manufacture, an assemblage of pg fibers comprising fibers of polymer of an a-monoolefin 5 containing from about 0.2% to about based on 2 i- Y 310 the weight of the polymer, of a carboxylic acid salt of 3 290 a metal selected from the group consisting of calcium,

MZetbylhemnwte 290 barium, iron, nickel, and cobalt, said salt having a melt- 2; i3ififif$pgg 288 ing temperature below the temperature at which the fiber 7- 0.92% 2-ethylhexanoic acid 10 is spun, said fibers being heat-bonded to other fibers in Liizdfiiffiitfi:fittttfi ttittffi 290 Said assemblage at Points of Contact therewith- 2. The article of claim 1 wherein the assemblage is EXAMPLES 9 TO 13 a nonwoven fabric.

The examples in the following table illustrate the de- The amele of elalm 1 wherem the 'monoolefin 1S sirable properties of nonwoven fabrics produced from 15 Propylenecrimped staple fiber on the yarn of Example 1. The Webs aetlele of elalm 1 Wherem e eatboxyheeeld for an the fabrics were prepared by a Standard sarding salt is the nickel salt of a fatty carboxylic acid containing or air laying operation, the fibers being laid upon a flat 8 to 18 earben atoms' backing. The fabrics, either with or without needle punch- The amele 0t elalm 4 Wherem the meket salt t ing, were next compressed under a cover at elevated tem- 20 a {mxture 0t mekel'z'ethylhexanoate and z'ethylhexanole perature to heat-soften the surfaces of the fiber and then aeld' cooled, whereby the heat-softened fiber surfaces solidified Process t Produemg bonded Structure i t to bond the fabrics at cross-over points. The products of eompnses tormmg an assemblage 0t fibers eofnpnsmg each of these examples were soft and fibrous and possessed fibers of a Polymer of an 'monoolefin eontemmg from good Strength about 0.2% to about 10% based on the weight of the The bonded fabrics were conditioned for at least 24 polymer of eereoxyhe e Salt metal seleeted from hours at 50% relative humidity and 73 F. and then tested the P calcwfll; barlumi mckel, and according to ASTM Method D 1117 63 to determine cobalt, said salt having a meltlng temperature below the their tensile strength, elongation and fabric weight. In detemperature at Wheh the fiber Spun, e sald assem' termining the tensile strength, the cut strip method blage an elevated temperature Whleh 15 below e (ASTM D-1117-63, section 6) was used. Test specimens crystalllne m ltlng temperature of the polymer but 18 were 1 x 6-inch strips which were tested in an Instron Suffieently elevated to reflder the surtaees of e fibers Tensile Tester with a 341mb draw Span, crosshead Speed tacky and heat-softened without substantially affecting the set at 12 inches per minute. Details as to the web preparafibrous Struetufe and the strength Propertles 531d fibers tion, fabric, and the test results obtained in these examand then eoolmg the assemblage whereby f heat'sott ples are tabulated below. Attempts to develop interfiber ened fibers f heat'bonded to other fibers the assem' bonding by fusing unmodified (no nickel salt additive) blage at Pomts of Contact therewlthpolypropylene fiber surfaces at cross-over points in the The Process of elalm 6 Wherem the 'monoolefin 1S manner of these examples were not successful. Bonding propyleneat temperatures and pressures low enough to develop soft, 40 The Process of dam 7 Whefeln the fibers are fabric-like structures gave very weak nonwoven fabrics. Oriented- Increasing the temperature and pressure high enough to 9. The process of claim 8 wherein the carboxylic acid develop the degree of fiber crossover point bonding needed salt is a mixture of nickel-2-ethylhexanoate and 2-ethylfor acceptable strength gave harsh plastic-like products. hexanoic acid.

TABLE II Needle punch Elongation Tensile Ex. N0. Web preparation Sample Wt, density at break strength Bonding conditions ozJsq. yd. (punches/in?) (percent) (lbs./in./oz./

sq. yd.)

9 Carded 5.06 0 11 5. 10 Hydraulic press; 220 psi. for seconds at 300 F.

ollowed by 2 minute cooling to room temperaure. 8. 45 1, 890 66 12. 9 Drum dryer at 325 F. for 4 minutes. 6. 76 0 35 7. 0 4 calendar rolls at 315, 318, 70, and 70 F., respectively, each traveling at 3 ttJmin. 6.36 700 49 9.8 4 calendar rolls at 325, 325, 105, and 70 F., respectively, each traveling at 3 itJmin. l3 Carded and tufted. 6. 70 2, 500 72 8. 4 Drum dryer at 325 F. for 4 minutes.

References Cited UNITED STATES PATENTS 3,049,466 8/1962 Erlich 16-1-150 3,322,607 5/1967 Jung 16 1-150 MORRIS SUSSMAN, Primary Examiner.

us. 01. XR. 

1. AS AN ATRICLE OF MANUFACTURE, AN ASSEMBLAGE OF FIBERS COMPRISING FIBERS OF POLYMER OF AN A-MONOOLEFIN CONTAINING FROM ABOUT 0.2% TO ABOUT 10%, BASED ON THE WEIGHT OF THE POLYMER, OF A CARBOYLIC ACID SALT OF A METAL SELECTED FROM THE GROUP CONSISTING OF CALCIUM, BARIUM, IRON, NICKEL, AND COBALT, SAID SALT HAVING A MELTING TEMPERATURE BELOW THE TEMPERATURE AT WHICH THE FIBER IS SPUN, SAID FIBERS BEING HEAT-BONDED TO OTHER FIBERS IN SAID ASSEMBLAGE AT POINTS OF CONTACT THEREWITH. 